That number does not seem particularly impressive, if it is accurate. Even "traditional" well-run enterprise IT organizations are often in the 1 admin/SRE to 600-ish machines, so I have a hard time seeing that Google can only do ~2x as good at their scale and with their level of focus.
1 SRE to 5k machines, 10k machines, that makes more sense to me.
Admittedly, I probably have a bad impression of enterprise from consulting because who would pay for automation consulting at $$$ / hr when you do it pretty well with existing resources in the first place?
It seems much easier in my opinion to scale a single function (search or tweet) than the kinds of tasks that a healthcare company has to do like say...scanning faxes from doctors, applying OCR and properly placing them into a pharmacy order system.
you can take a snapshot and say you are 1:n because today you have so many sre and so many machines, but it is very unlikely to be the same ratio down the road.
When you remove the VM smokescreen and count physical boxes it's more like 1 person/100 machines, which is abysmal. I've seen order-of-magnitude people efficiency increases with automation like we're discussing here.